Do-while loop execution model in PHP - Step-by-Step Execution

Concept Flow - Do-while loop execution model

Start

↓

Execute body

↓

Check condition

Yes| No↓

Repeat

The do-while loop runs the code inside the loop first, then checks the condition. If true, it repeats; if false, it stops.

Execution Sample

PHP

<?php
$i = 1;
do {
  echo $i . " ";
  $i++;
} while ($i <= 3);
?>

This code prints numbers 1 to 3 using a do-while loop.

Execution Table

Step	Variable i	Condition ($i <= 3)	Action	Output
1	1	1 <= 3 is True	Print 1, increment i to 2	1
2	2	2 <= 3 is True	Print 2, increment i to 3	2
3	3	3 <= 3 is True	Print 3, increment i to 4	3
4	4	4 <= 3 is False	Exit loop

💡 i reaches 4, condition 4 <= 3 is False, loop stops

Variable Tracker

Variable	Start	After 1	After 2	After 3	Final
i	1	2	3	4	4

Key Moments - 2 Insights

Why does the loop body run even when the condition is false initially?

Because in a do-while loop, the body runs first before the condition is checked, as shown in step 1 of the execution_table.

When does the loop stop running?

The loop stops when the condition becomes false, which happens at step 4 when i is 4 and 4 <= 3 is false.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of i at step 3?

A 4

B 2

C 3

D 1

💡 Hint

Check the 'Variable i' column at step 3 in the execution_table.

At which step does the condition become false and the loop stops?

A Step 2

B Step 4

C Step 3

D Step 1

💡 Hint

Look at the 'Condition' column in the execution_table where it says false.

If the initial value of i was 5, how many times would the loop body execute?

A 1 time

B 0 times

C 3 times

D Infinite times

💡 Hint

Remember do-while runs the body once before checking condition, see concept_flow.

Concept Snapshot

do-while loop syntax in PHP:
do {
  // code to run
} while (condition);

Runs loop body first, then checks condition.
Repeats if condition true, stops if false.
Always runs at least once.

Full Transcript

A do-while loop in PHP runs the code inside the loop first, then checks the condition. If the condition is true, it repeats the loop. If false, it stops. This means the loop body always runs at least once, even if the condition is false initially. In the example, the variable i starts at 1. The loop prints i, then increases it by 1. It repeats while i is less than or equal to 3. When i becomes 4, the condition fails and the loop stops. This is shown step-by-step in the execution table and variable tracker.